1. Field of the Invention
The invention relates to a backlight module. More particularly, the invention relates to an edge-type backlight module.
2. Description of Related Art
In recent years, liquid crystal displays (LCDs) that have been developed toward full-color display gradually replace a conventional cathode ray tube (CRT) display and have become a main stream of displays in the market due to the advantages of a low operation voltage, non-radiation, light weight, small volume occupancy, and so forth. The LCDs are non-self-illuminating displays, and therefore display functions of the LCDs are achieved when required light is provided by a backlight module. With increasing consciousness of environmental protection, cold cathode fluorescent lamps (CCFLs) serving as light-emitting devices in a conventional backlight module are gradually replaced by light-emitting diode (LED) devices because the LED devices are more friendly to environment. When the LED devices are applied in the backlight module, e.g., an edge-type backlight module, the LED devices are usually mounted on a bar-shaped printed circuit board (PCB) to form an LED light bar. The LED light bar is often electrically connected to a control circuit board through a flexible printed circuit (FPC).
FIG. 1 is a schematic top view illustrating a conventional edge-type backlight module. FIG. 2A and FIG. 2B are schematic cross-sectional views illustrating different types of conventional edge-type backlight modules. With reference to FIG. 1 and FIG. 2A, the conventional edge-type backlight module 100 includes a light guide plate (LGP) 110, a light source 120, a frame 130, and a back bezel 140. The LGP 110 is configured on the back bezel 140. Besides, the LGP 110 has a top light-emitting surface 112 and a light-incident side surface 114 connected to the top light-emitting surface 112. The top light-emitting surface 112 includes an effective illumination region 112b and a peripheral region 112a that is connected to the light-incident side surface 114.
It can be learned from FIG. 1 and FIG. 2A that the light source 120 is configured next to the light-incident side surface 114 to provide a light beam L. The light source 120 includes a circuit board 122 and a plurality of side-view LED devices 124. Each of the side-view LED devices 124 is configured on and electrically connected to the circuit board 122. That is to say, the light source 120 is a side-view LED light bar.
As shown in FIG. 1, a pitch between any two adjacent LED devices 124 of the conventional light source 120 is P, and the shortest light path from the light-emitting surface of each of the LED devices 124 to the edge of the effective illumination region 112b is A. In order to uniformize the luminance of the effective illumination region 112b, users determine the optimal A/P ratio based on the divergence angle of the light beam L of the LED devices 124. However, the LCD has been developed to comply with the requirement for the slim border design, and therefore the shortest light path A from the light-incident surface of each of the LED devices 124 to the edge of the effective illumination region 112b needs to be further shortened. When the A/P ratio is overly low, dark and bright hot spots are generated at the effective illumination region 112b close to the light-incident side surface 114. The dark regions shown in FIG. 1 refer to regions with low luminance. The hot spots can be removed by shortening the pitches P, while more of the LED devices 124 are required when the pitches P are shortened. As such, manufacturing costs are increased. Apparently, the edge-type backlight module 100 depicted in FIG. 2A cannot be designed in consideration of both the A/P ratio and the manufacturing costs.
With reference to FIG. 2B, a top-view LED light bar serves as the light source 120 of the edge-type backlight module 100′. Specifically, the light source 120 includes a circuit board 122 and a plurality of top-view LED devices 124′. Each of the top-view LED devices 124′ is configured on and electrically connected to the circuit board 122. To further improve heat dissipation efficiency of the top-view LED devices 124′, a heat sink HS is frequently employed to dissipate heat generated by the top-view LED devices 124′.
Based on the above, in the edge-type backlight modules 100 and 100′ respectively depicted in FIG. 2A and FIG. 2B, a width W (which is usually referred to as the distance from the edge of the effective illumination region 112b to the edge of the edge-type backlight modules 100 and 100′) of the frame is closely related to the A/P ratio. That is to say, the shortest light path A from the light-emitting surface of each of the LED devices 124 to the edge of the effective illumination region 112b is directly subject to the width W of the frame. Accordingly, how to increase the A/P ratio in compliance with the requirement for slim border design without significantly increasing the manufacturing costs becomes an important issue to be resolved.